Use of cannabis enhances attentional inhibition.

Objective: Orienting attention to an irrelevant location hampers the response to subsequent targets presented at that location in relation to novel, not previously attended, locations. This inhibitory effect has been named inhibition of return. We conducted an experiment to study the temporal course of inhibition of return in users of cannabis.

Method: Twenty-five cannabis users who self-reported a regular frequency of cannabis use in joints per month, and 26 drug-free controls participated in the study. We employed a typical inhibition of return task with a single cue and manipulated the time interval between the onset of the cue and the target (150, 350, 550, 1500, and 2550 ms). Participants were asked to detect the onset of the target regardless of its location.

Results: The group of cannabis users showed a significantly greater overall inhibition relative to the group of nonusers. Furthermore, inhibition of return appeared earlier (at the 350 ms cue-target interval) in the user group.

Conclusions: This is the first study to show that attentional inhibition is enhanced in cannabis users. More research is needed to determine whether greater inhibition represents an advantage or disadvantage for visual search performance of cannabis users.